Chloroprene latex composition, process for producing the same, and adhesive composition comprising the same

ABSTRACT

A chloroprene latex composition wherein the gel content of the chloroprene polymer is from 3 to 40 wt %, and the weight average molecular weight of the sol content is at least 400,000, and a chloroprene latex is presented which is excellent in the initial adhesive performance and normal adhesive performance and which has a good balance of heat resistance, water resistance, etc. with the adhesive properties.

TECHNICAL FIELD

The present invention relates to a polychloroprene latex compositionuseful as an adhesive, and a method for its production and an adhesivecomposition employing it. More particularly, it relates to a chloroprenelatex composition which is excellent in the initial adhesive performanceand which is excellent in the balance of the heat resistance, waterresistance, etc. with the adhesive properties, and a method for itsproduction and an adhesive composition employing it.

BACKGROUND ART

Heretofore, adhesives using polychloroprene as a base were mainly of asolvent type. However, in recent years, demand for not employing asolvent has increased in view of problems such as toxicity, possibledanger of fire and environmental pollution by an organic solvent duringthe production or use of solvent type adhesives. As a method for notemploying a solvent, a method of substituting a latex adhesive for asolvent type adhesive is considered to be effective, and a study hasbeen actively conducted on latex adhesives using various polymers.

Among them, a chloroprene latex adhesive is coated on both adherends tobe bonded, such adhesive layers are dried and then bonded, whereby itexhibits high adhesiveness immediately after the bonding. From such acharacteristic, it is expected to be useful as an aqueous contact typeadhesive, but on the other hand, it is not necessarily satisfactory inthe initial adhesive performance and in the balance of the heatresistance, water resistance, etc. with the adhesive properties, andimprovements in this respect have been desired.

For example, JP-B-51-39262 discloses a method for producing apolychloroprene latex adhesive, wherein from 3 to 5 parts by weight of along chain fatty acid or a rosinate is used as an emulsifier, per 100parts by weight of chloroprene, and the monomer is polymerized at atemperature lower than 20° C. in an alkaline emulsion in the presence offrom 0.09 to 0.15 part by weight of n-dodecyl mercaptan, andpolymerization is terminated when the conversion of the monomer reachesfrom 90 to 98% to obtain a latex of polychloroprene containing from 40to 90 wt % of a gel content, and a tackifier resin is blended thereto.However, latexes prepared in accordance with Examples of suchpublication lack in the contact property, and in order to make contactadhesion possible, a large amount of a tackifier resin is required to beadded, and it takes time for the development of the strength, and theinitial adhesive performance has not been necessarily satisfactory.

The present invention is intended to solve such problems of the priorart and to provide a chloroprene latex composition which is excellent inthe initial adhesive performance and which is excellent also in thebalance of the heat resistance and the water resistance, a method forits production and an adhesive composition employing it.

DISCLOSURE OF THE INVENTION

The present inventors have conducted extensive studies to solve theabove problems, and as a result, have found it possible to obtain achloroprene latex adhesive composition which is excellent in the initialadhesive performance and which is excellent also in the balance of theheat resistance, water resistance, etc. with the adhesive properties bya chloroprene latex composition having a certain specific amount of agel content and a certain specific molecular weight of sol, and haveaccomplished the present invention.

Namely, the present invention provides a chloroprene latex compositioncomprising a chloroprene polymer containing from 3 to 40 wt % of a gelcontent and having a weight average molecular weight of sol of at least400,000, and a method for its production and an adhesive compositionemploying it.

Further, the present invention provides the above-mentioned chloroprenelatex composition wherein the chloroprene polymer is one obtained bypolymerizing chloroprene, using a rosinate as an emulsifier, in thepresence of a chain transfer agent at a temperature lower than 30° C. toa conversion of the monomer of from 80 to 95%, and the solid contentconcentration in the latex is from 45 to 65 wt %.

Further, the present invention provides the above-mentioned chloroprenelatex composition wherein the emulsifier is potassium rosinate, and thepolymerization is carried out in the presence of excess potassiumhydroxide, a method for producing such a chloroprene latex composition,and an adhesive composition obtained by adding a tackifier resin to sucha chloroprene latex composition.

Now, the present invention will be described in detail. The chloroprenepolymer in the present invention is a homopolymer of2-chloro-1,3-butadiene (hereinafter referred to as chloroprene), or acopolymer obtained by copolymerizing chloroprene with at least onemonomer copolymerizable with chloroprene.

As the monomer copolymerizable with chloroprene in the presentinvention, 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene,butadiene, isoprene, styrene, acrylonitrile, acrylic acid and itsesters, methacrylic acid and its esters, may, for example, be mentioned,and if necessary, two or more types may be employed.

The gel content in the chloroprene polymer in the present invention ismeant for the content of a component insoluble in a toluene solvent, andthe sol is meant for a soluble component. In the chloroprene polymer inthe present invention, the gel content is required to be within a rangeof from 3 to 40 wt %.

Further, the gel content was measured by the following method. The latexwas freeze-dried (the weight was A) and dissolved in toluene at 23° C.for 20 hours (to adjust the concentration to 0.6 wt %), and using acentrifugal separator, and further using a 200 mesh metal net, theinsoluble content i.e. the gel was separated. The gel content was driedin air and then dried in an atmosphere of 110° C. for one hour (theweight was B). The gel content was calculated by the following formula.

Gel content=B/A×100(%)

Further, in the present invention, the weight average molecular weightof the sol in the chloroprene polymer i.e. the toluene solvent-solublecomponent, plays an important role, and the weight average molecularweight of the chloroprene polymer of the present invention is requiredto be at least 400,000. A preferred range of the weight averagemolecular weight is from 400,000 to 1,200,000.

In the present invention, the gel content and the weight averagemolecular weight of the sol in the chloroprene polymer are defined asmentioned above, for the following reasons.

Development of the excellent initial adhesive performance in the presentinvention is attributable to the fact that the chloroprene polymercontains a large amount of sol excellent in molecular motion.Accordingly, fusion of chloroprene molecular chains at the adhesiveinterface takes place swiftly to instantaneously develop the adhesivestrength, whereby it is possible to develop an excellent initialadhesive performance. If the gel content of the chloroprene polymerexceeds 40 wt %, this initial adhesive performance decreasessubstantially, such being undesirable.

On the other hand, in chloroprene latex adhesives which were commonlyknown, a chloroprene polymer having a low gel content tended to be poorin heat resistance, and the balance of the heat resistance with theinitial adhesive property was poor. In the present invention, anexcellent balance of the initial adhesive performance and the heatresistance has been made possible by adjusting the gel content of thechloroprene polymer to be from 3 to 40 wt % and adjusting the weightaverage molecular weight of the sol to be at least 400,000. If the gelcontent is less than 3 wt %, or the weight average molecular weight ofthe sol is less than 400,000, the heat resistance decreasessubstantially.

Further, when a still higher balance of the initial adhesive propertyand the heat resistance is required in the present invention, it ispreferred that the gel content is from 5 to 30 wt %, and the weightaverage molecular weight of the sol is at least 500,000.

To obtain such a chloroprene latex adhesive, a well known polymerizationmethod may be employed for the preparation so that the gel content ofthe chloroprene polymer would be from 3 to 40 wt % and the weightaverage molecular weight of the sol would be at least 400,000. However,as a high level of molecular control is required, it is preferred tocarry out the preparation by the following method.

To obtain a chloroprene latex, a method of carrying out radicalpolymerization in an aqueous emulsion is a simple and industriallyadvantageous method. As the emulsifier to be used at that time, anemulsifier commonly employed for emulsion polymerization of chloroprenecan be used. For example, an anionic emulsifier such as a rosinate, afatty acid salt, an alkyl sulfonate such as sodium alkyl benzenesulfonate, an alkyl sulfate such as sodium lauryl sulfate, a non-ionicemulsifier, a cationic emulsifier, or a water-soluble polymer such aspolyvinyl alcohol, may be mentioned. These emulsifiers may be used aloneor in a combination of two or more of them. However, from the viewpointof the water resistance of the obtained latex or control of thepolymerization, it is preferred to use a rosinate, a fatty acid salt, ananionic emulsifier or a cationic emulsifier as the main component, andit is further preferred to employ a rosinate.

It is possible to control the molecular weight of the sol and the amountof the gel content in the chloroprene polymer by adjusting {circlearound (1)} the use and the amount of use of the chain transfer agent,{circle around (2)} the polymerization temperature and {circle around(3)} the final conversion of the monomer.

Firstly, the chain transfer agent is not particularly limited so long asit is one commonly employed for the production of a chloroprene polymer.For example, a known chain transfer agent, such as a long chain alkylmercaptan such as n-dodecyl mercaptan or tert-dodecyl mercaptan, adialkyl xanthogen disulfide such as diisopropyl xanthogen disulfide ordiethyl xanthogen disulfide, or iodoform, may be used.

Next, the polymerization temperature is preferably within a range offrom 0 to 55° C. from the viewpoint of control of the polymerization.However, to obtain a chloroprene polymer having a gel content of from 3to 40 wt % and a weight average molecular weight of sol of at least400,000 in the present invention, it is preferred to adjust thepolymerization temperature to a level of from 5 to 30° C., and it ismore preferred to carry out the polymerization at a low temperature offrom 5 to 20° C. By carrying out the polymerization at a lowertemperature, it is possible to suppress the gel content to a low leveland to increase the weight average molecular weight of the sol. Further,by lowering the polymerization temperature, it is possible to increasethe 1,4-trans structure in the chloroprene main chain and to obtain achloroprene polymer having high crystallinity. Accordingly, afterapplying the adhesive, crystallization of chloroprene will proceed,whereby it is possible to obtain an adhesive layer having a highcohesive force.

The final conversion of the monomer is preferably within a range of from80 to 95%. By adjusting the final conversion of the monomer to be withinthis range, it is possible to control the chloroprene polymer to havethe desired gel content and the desired molecular weight of sol. Tocontrol the final conversion of the monomer to be within this range, apolymerization terminator such as phenotiazine, hydroxylamine ortert-butyl catechol may be added to terminate the polymerization so thatthe prescribed final conversion of the monomer is obtained.

Further, when the chloroprene polymer is a copolymer, the conversion ofthe monomer is represented by the weight% of the polymerized monomersbased on the entire monomers involved in the copolymerization.

Further, the amount of the chain transfer agent may be adjusted so thatthe intended gel content and molecular weight of sol can be attainedwithin such a range of the final conversion of the monomer. For example,when n-dodecyl mercaptan is used as the chain transfer agent, such canbe attained by using it in an amount of from 0.06 to 0.15 parts byweight per 100 parts by weight of chloroprene and carrying out thepolymerization so that the final conversion of the monomer is within arange of from 80 to 95%.

In the present invention, the solid content concentration of thechloroprene latex is preferably within a range of from 45 to 65 wt %,more preferably from 50 to 65 wt %, still more preferably within a rangeof from 55 to 65 wt %. The higher the solid content concentration, thebetter the initial adhesive property of the latex. Particularly undersuch a condition that complete drying can not be carried out, i.e. in acase where bonding is required to be carried out in a state where slightmoisture remains, the effect for improving the initial adhesiveperformance by a high solid content concentration, will be remarkable.

Further, to make such a highly concentrated latex easy to handle and ina stabilized state, it is preferred to carry out polymerization ofchloroprene in the presence of potassium rosinate and a large excessamount of potassium hydroxide, as emulsifiers. At that time, the amountof the rosinate is preferably within a range of from 1 to 10 parts byweight, more preferably from 3 to 5 parts by weight, per 100 parts byweight of chloroprene, and the amount of potassium hydroxide ispreferably from 0.3 to 2 parts by weight, more preferably from 0.6 to1.5 parts by weight, per 100 parts by weight of chloroprene. It isthereby possible to obtain a chloroprene latex which is excellent in lowtemperature stability or stability against phase separation when left tostand and which is also excellent in storage stability. For example, itis common to employ a method of adding sodium rosinate or sodiumhydroxide as the excess alkali, but in such a case, as the concentrationincreases, the standing still stability or the low temperature stabilityis likely to deteriorate, which may bring about a practical trouble.

In the chloroprene latex of the present invention, a pH controllingagent, an antifreezing agent, etc., may be added after thepolymerization. Further, at the time of its use, depending upon thecharacteristics required in its application, it is preferred to add asuitable amount of a rosinate resin, a terpene phenoric resin, acoumarone-indene resin, an aliphatic hydrocarbon resin or an aromaticpetroleum resin as a tackifier resin and use it as an adhesive. Inaddition to these resins, a metal oxide such as zinc oxide, an inorganicfiller such as calcium carbonate or silica, a plasticizer or a softeningagent, such as dibutyl phthalate or process oil, further variousantioxidant agents or vulcanization accelerators, curing agents such asisocyanates, thickners, etc., may optionally be incorporated.

The chloroprene latex adhesive obtained by the present invention isuseful for bonding or joining the same or different types of materialssuch as paper, wood, cloth, leather, rubber, plastics, foams, potteries,glass, ceramics or metals. The application method for the bonding maybe, for example, by brush coating, pallet coating, spray coating or rollcoater coating. Further, bonding in a wet state is possible, anexcellent initial adhesive performance can be obtained in either suchbonding or contact bonding after drying, and the balance of the heatresistance, water resistance, etc., with the adhesive properties, isalso excellent.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in detail with reference toExamples, but these Examples by no means restrict the present invention.Further, parts and % in the following description will be represented byweight.

EXAMPLE 1

Using a reactor having an internal capacity of 3 l, in a nitrogenstream, 100 parts of water, 4 parts of disproportionated rosin acid, 1.0part of potassium hydroxide and 0.8 part of a sodium salt of aformaldehyde/naphthalene sulfonic acid condensate, were charged anddissolved, and then, 100 parts of a chloroprene monomer and 0.1 part ofn-dodecyl mercaptan were added with stirring. Using potassium persulfateas an initiator, polymerization was carried out in a nitrogen atmosphereat 10° C., and when the conversion of the monomer reached 90%, anemulsion of phenothiazine was added to terminate the polymerization. Anunreacted monomer was removed under reduced pressure, to obtain achloroprene latex. Further, the water was evaporated under reducedpressure to carry out concentration, whereby the solid contentconcentration was adjusted to be 60 wt %.

Then, with respect to this chloroprene latex, an adhesive compositionwas prepared in the formulation as identified in Table 1, and theadhesive properties were evaluated by the following methods.

Initial Adhesive Strength

On each of two sheets of canvas (25×150 mm), 200 g of the adhesivecomposition was coated by a brush and dried for 6 minutes in anatmosphere of 70° C. Then, the coated sides were bonded, followed bypressing by a hand roller.

Upon expiration of 10 minutes after the pressing, the 180° peel strengthwas measured by a tensile tester at a tensile speed of 50 mm/min.

Final State Adhesive Strength

On each of two sheets of canvas (25×150 mm), 200 g of the adhesivecomposition was coated by a brush and dried for 6 minutes in anatmosphere of 70° C. Then, the coated sides were bonded, followed bypressing by a hand roller.

Upon expiration of five days after the pressing, the 180° peel strengthwas measured by a tensile tester at a tensile speed of 50 mm/min.

Heat Creep Resistance Test

On each of two sheets of canvas (25×150 mm), 200 g of the adhesivecomposition was coated by a brush and dried for 6 minutes in anatmosphere of 70° C. Then, the coated sides were bonded, followed bypressing by a hand roller.

Upon expiration of 24 hours after the pressing, it was left to stand for20 minutes in an atmosphere of 80° C. Then, in an atmosphere of 80° C.,200 g of a load was applied in the same manner as in the 180° peel testand left to stand for 30 minutes, whereby the length (mm) of thedisplacement of canvas was measured.

Water Resistance Strength

On each of two sheets of canvas (25×150 mm), 200 g of the adhesivecomposition was coated by a brush and dried for 6 minutes in anatmosphere of 70° C. Then, the coated sides were bonded, followed bypressing by a hand roller.

Upon expiration of 24 hours after the pressing, it was immersed in waterfor 2 days. Then, the 180° peel strength was measured by a tensiletester at a tensile speed of 50 mm/min.

Further, the gel content of the obtained chloroprene polymer and themolecular weight of the sol were measured in accordance with thefollowing methods.

Measurement of the Gel Content

The latex sample was freeze-dried and accurately weighed to obtain A. Itwas dissolved in toluene at 23° C. for 20 hours (to a concentration of0.6%), and using a centrifugal separator and further a metal net of 200mesh, the gel was separated. The gel content was dried in air and thendried in an atmosphere of 110° C. for 1 hour and accurately weighed toobtain B.

The gel content was calculated in accordance with the following formula.

Gel content=B/A×100(%)

Measurement of the Molecular Weight

GPC measurement was carried out under the following conditions. Themolecular weight was calculated as polystyrene.

The sample was prepared by forming the separated sol into a 0.1% THFsolution.

Column: PL gel 10 μm GUARD+PL gel 10 μm Mixed-B×3 columns

Column size: 7.5 mm φ×50 mm (GUARD), 7.5 mm φ×300 mm (Mixed-B)

Column temperature: 35° C., Solvent:THF,

Flow out rate: 1 ml/min

Detector: SIMADZU RID-6-A

EXAMPLE 2

In Example 1, the amount of n-dodecyl mercaptan added was changed to0.06 part, and polymerization was carried out and measurements of theadhesive properties, the gel content and the molecular weight werecarried out in the same manner as in Example 1.

EXAMPLE 3

In Example 1, the amount of n-dodecyl mercaptan was changed to 0.15part, and polymerization was carried out and measurements of theadhesive properties, the gel content and the molecular weight werecarried out in the same manner as in Example 1.

EXAMPLE 4

In Example 1, the final conversion of the monomer was adjusted to 85%,and polymerization was carried out and measurements of the adhesiveproperties, the gel content and the molecular weight were carried out inthe same manner as in Example 1.

EXAMPLE 5

In Example 1, the final conversion of the monomer was adjusted to 93%,and polymerization was carried out and measurements of the adhesiveproperties, the gel content and the molecular weight were carried out inthe same manner as in Example 1.

EXAMPLE 6

In Example 1, the polymerization temperature was changed to 20° C., andpolymerization was carried out and measurements of the adhesiveproperties, the gel content and the molecular weight were carried out inthe same manner as in Example 1.

Comparative Example 1

In Example 1, the amount of n-dodecyl mercaptan added was changed to0.04 part, and polymerization was carried out and measurements of theadhesive properties, the gel content and the molecular weight werecarried out in the same manner as in Example 1.

Comparative Example 2

In Example 1, the amount of n-dodecyl mercaptan added was changed to0.25 part, and polymerization was carried out and measurements of theadhesive properties, the gel content and the molecular weight werecarried out in the same manner as in Example 1.

Comparative Example 3

In Example 1, the final conversion of the monomer was adjusted to 70%,and polymerization was carried out and measurements of the adhesiveproperties, the gel content and the molecular weight were carried out inthe same manner as in Example 1.

Comparative Example 4

In Example 1, the final conversion of the monomer was adjusted to 97%,and polymerization was carried out and measurements of the adhesiveproperties, the gel content and the molecular weight were carried out inthe same manner as in Example 1.

Comparative Example 5

In Example 1, the polymerization temperature was changed to 40° C., andpolymerization was carried out and the measurements of the adhesiveproperties, the gel content and the molecular weight were carried out inthe same manner as in Example 1.

The results of the foregoing Examples are shown in Table 1, and theresults of the Comparative Examples are shown in Table 2.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Latex Chloroprene 100 100100 100 100 100 formulation n-dodecyl mercaptan 0.10 0.06 0.15 0.10 0.150.10 (parts by Pure water 100 100 100 100 100 100 weight)Disproportionated rosin 4 4 4 4 4 4 acid Potassium hydroxide 1.0 1.0 1.01.0 1.0 1.0 Sodium salt of 0.8 0.8 0.8 0.8 0.8 0.8formaldehyde/naphthalene sulfonic acid condensate Latex Polymerization10 10 10 10 10 20 polymerization temperature ° C. condition Conversionof the 90 90 90 85 93 90 monomer % Latex Solid content 60 60 60 60 60 60properties concentration % Gel content % 10 34 5 5 25 30 Mw of sol ×10⁻⁴65 50 60 75 55 50 Adhesive blend Latex 100 100 100 100 100 100formulation Antioxidant Note 1 1 1 1 1 1 1 (parts by Zinc white Note 2 33 3 3 3 3 weight) Resin Note 3 50 50 50 50 50 50 Results of Initialadhesive 4.5 3.5 4.5 4.8 4.5 4.0 adhesive tests strength N/mm Finaladhesive strength 5.5 5.0 5.5 5.7 5.5 5.5 N/mm Heat creep resistance mm1 0 3 3 2 1 Water resistance 4.9 4.3 4.9 5.0 4.7 4.5 strength N/mm Note1 2,6-tert-butyl-4-methylphenol Note 2 AZ-SW, manufactured by OsakiKogyo K.K. Note 3 Tamanol E-100, manufactured by Arakawa Kagaku KogyoK.K.

TABLE 2 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5Latex Chloroprene 100 100 100 100 100 formulation n-dodecyl mercaptan0.04 0.25 0.10 0.10 0.10 (parts by Pure water 100 100 100 100 100weight) Disproportionated rosin 4 4 4 4 4 acid Potassium hydroxide 1.01.0 1.0 1.0 1.0 Sodium salt of 0.8 0.8 0.8 0.8 0.8formaldehyde/naphthalene sulfonic acid condensate Latex Polymerization10 10 10 40 40 polymerization temperature ° C. condition Conversion ofthe 90 90 70 97 90 monomer % Latex Solid content 60 60 60 60 60properties concentration % Gel content % 45 0 0 70 50 Mw of sol ×10⁻⁴ 5035 65 35 45 Adhesive blend Latex 100 100 100 100 100 formulationAntioxidant Note 1 1 1 1 1 1 (parts by Zinc oxide Note 2 3 3 3 3 3weight) Resin Note 3 50 50 50 50 50 Results of Initial adhesive 1.1 3.54.5 0.8 0.7 adhesive tests strength N/mm Final adhesive strength 5.0 4.55.7 5.0 4.7 N/mm Heat creep resistance mm 1 Peeled Peeled 0 1 Waterresistance 4.0 4.8 4.9 3.5 2.5 strength N/mm Note 12,6-tert-butyl-4-methylphenol Note 2 AZ-SW, manufactured by Osaki KogyoK.K. Note 3 Tamanol E-100, manufactured by Arakawa Kagaku Kogyo K.K.

From comparison between the foregoing Examples and Comparative Examples,it is evident that the chloroprene latex adhesives employing thechloroprene latex compositions of the present invention are excellent inthe initial adhesive properties and have a good balance of the heatresistance, water resistance, etc. with the adhesive properties. Thus,it is possible to provide chloroprene latex compositions which areparticularly suitable for bonding of wood materials such as plywood,bonding of urethane foams or bonding of paper materials, etc.

What is claimed is:
 1. A latex composition comprising a chloroprenepolymer or copolymer having a gel content of from 3 to 40 wt % andhaving a weight average molecular weight of sol of at least 400,000,wherein the chloroprene polymer or copolymer is obtained by polymerizingchloroprene or by copolymerizing chloroprene with a comonomer with arosinate emulsifier in the presence of a chain transfer agent at atemperature ≦30° C. to a monomer conversion of from 80 to 95%, whereinthe solid content concentration in the latex is from 45 to 65 wt %. 2.The latex composition according to claim 1, wherein said emulsifier ispotassium rosinate and the polymerization is carried out in the presenceof excess potassium hydroxide.
 3. An adhesive composition obtained byadding a tackifier resin to said latex composition as defined in any oneof claims 1 to
 2. 4. A method for producing a latex compositioncomprising: polymerizing chloroprene or copolymerizing chloroprene witha comonomer with a rosinate emulsifier in the presence of a chaintransfer agent at a temperature ≦30° C. to a monomer conversion of from80 to 95%, and adjusting the solid content concentration in the latex tobe from 45 to 65 wt %.
 5. The method according to claim 4, wherein saidtemperature is from 5 to 30° C.
 6. The method according to claim 4,wherein said temperature is from 5 to 20° C.
 7. The method according toclaim 4, wherein said emulsifier is potassium rosinate and saidpolymerizing or copolymerizing is carried out in the presence of excesspotassium hydroxide.